Sharing ground wire between two dedicated circuits

Here you go.  This is the best treatise on wiring for AV/2-channel audio that I have seen.  Basically, it is the wiring scheme I have used for years.  This works.

I would never waste any money on Romex. An connecting grounds any where besides earth creates a ground loop.

Ground Connects to a stake in the dirt, why don't you like romex?

fuzztone

... connecting grounds any where besides earth creates a ground loop.

It’s not clear what you’re trying to say. A ground loop occurs when there are two or more paths to ground at different potential (voltage). You can have a dozen ground paths and if they’re all at the same potential you’ll have no issue.

In the US, a residential system’s safety ground will be bonded to the service panel’s neutral buss bar, which is also bonded to the electric utility’s neutral.

So it sounds like having an insulated ground back to the panel doesn't matter.  What about interference, all that noise and crap being diverted back to the panel via ground.  Why would I want noise from in uninsulated ground to be used???